This application is related to and claims priority from Japanese Patent Applications No. Hei. 11-307493 filed on Oct. 28, 1999, No. 2000-17816 filed on Jan. 21, 2000 and No. 2000-93013 filed on Mar. 28, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to a refrigerant cycle system with a super-critical refrigerant pressure, more particularly, relates to control operation of both a compressor and a pressure control valve of the refrigerant cycle system.
2. Description of Related Art
In a conventional super-critical refrigerant cycle described in JP-A-7-294033, an opening degree of a decompressing unit is controlled based on a refrigerant temperature at an outlet side of a radiator. When capacity of the super-critical refrigerant cycle is controlled only by the decompressing unit (i.e., pressure control valve), it is necessary to increase a refrigerant pressure at a high-pressure side by reducing the opening degree of the decompressing unit for increasing the capacity (e.g., cooling capacity and heating capacity). However, when the refrigerant pressure at the high-pressure side is increased, the efficiency of a compressor is decreased, and effective coefficient of performance of the super-critical refrigerant cycle is deteriorated.
In view of the foregoing problems, it is an object of the present invention to provide a refrigerant cycle system which provides necessary capacity of components of a super-critical refrigerant cycle while preventing coefficient of performance of the super-critical refrigerant cycle from being deteriorated.
According to the present invention, a refrigerant cycle system includes a compressor for compressing refrigerant and discharging refrigerant with a pressure higher than the critical pressure, a radiator for cooling refrigerant discharged from the compressor, a pressure control valve for decompressing refrigerant flowing from the radiator and being disposed to control a pressure of high-pressure side refrigerant from the compressor to a position before being decompressed, an evaporator for evaporating refrigerant decompressed in the pressure control valve, and a control unit which controls both a refrigerant amount discharged from the compressor and an opening degree of the pressure control valve. Because the control unit controls the refrigerant amount discharged from the compressor while controlling the opening degree of the pressure control valve, necessary capacity of components can be obtained in the refrigerant cycle, and coefficient of performance of the refrigerant cycle is prevented from being deteriorated.
Preferably, the control unit controls the refrigerant amount discharged from the compressor and the opening degree of the pressure control valve based on based on theoretical coefficient of performance of the refrigerant cycle and efficiency of the compressor. Therefore, the coefficient of performance of the refrigerant cycle can be improved while efficiency of the compressor can be improved.
Effective coefficient of performance of the refrigerant cycle is calculated based on a moving heat quantity moved from the evaporator to the radiator of the refrigerant cycle and a consumed power consumed by the compressor, and the control unit controls the refrigerant amount discharged from the compressor and the opening degree of the pressure control valve based on the calculated effective coefficient of performance of the refrigerant cycle. Therefore, the effective coefficient of performance of the refrigerant cycle can be improved.
Preferably, the control unit controls at least one of the refrigerant amount discharged from the compressor and the opening degree of the pressure control valve so that the temperature of high-pressure side refrigerant is lower than a predetermined temperature. Therefore, it can prevent the components of the refrigerant cycle from being troubled by heat.
Preferably, the control unit controls the refrigerant amount discharged from the compressor and the opening degree of the pressure control valve so that a driving torque of the compressor is lower than a predetermined torque. Therefore, the refrigerant cycle can obtain a predetermined capacity while it can prevent the driving torque of the compressor from being excessively increased.
When a temperature difference, between a refrigerant temperature at an outlet of the radiator and a temperature of a fluid passing through the radiator to perform a heat exchange with refrigerant, is equal to or larger than a predetermined temperature difference, the control unit controls the pressure control valve to have a refrigerant pressure at the outlet of the radiator, larger than a target refrigerant pressure determined based on the refrigerant temperature at the outlet of the radiator, while controlling the refrigerant amount discharged from the compressor to be decreased. Therefore, heat-exchanging effect of the radiator is improved while heating capacity due to the radiator can be prevented from being lowered.
Preferably, when the refrigerant cycle system is applied to an air conditioner, the control unit controls the refrigerant amount discharged from the compressor, while controlling the pressure control valve so that the pressure of the high-pressure side refrigerant becomes a target pressure determined based on temperature of outside air, when outside air is introduced into the radiator through an outside air passage. Therefore the control of the pressure control valve can be made simple.
Further, the refrigerant cycle system further includes an accumulator having a tank portion into which refrigerant from the evaporator flows to be separated into gas refrigerant and liquid refrigerant, and a flow control member for controlling an amount of liquid fluid, including lubrication oil and liquid refrigerant, flowing from the accumulator to the compressor. The tank portion of the accumulator has an upper outlet through which the gas refrigerant is sucked into the compressor from an upper side of the tank portion, and a lower outlet through which the liquid fluid is sucked into the compressor from a lower side of the tank portion. In the refrigerant cycle system, the flow control member controls the amount of liquid fluid flowing from the lower side of the tank portion into the compressor. Therefore, the lubrication oil contained in the liquid fluid can be variably supplied to the compressor from the accumulator in accordance with the rotation speed of the compressor or the refrigerant amount discharged from the compressor. Because the liquid fluid supplied from the accumulator to the compressor is increased when the refrigerant temperature discharged from the compressor is increased, it can prevent the compressor from being troubled even when the temperature of refrigerant discharged from the compressor is greatly increased.